Producing nitrogen and hydrogen mixtures



Patented Feb. 16, 1932 "-Un1rso STATES nanrn n nonsn, or CHARLESTON,wEs'r VIRGINIA, AssrGNonf Bi z jninslvn Assisti- MENTS, TO I; I. no PONTDE nnmouns & COMPANY, or wrr mme'ron, DELAWARE,

1 A o'o'RPonA'rIoN or DELAWARE PRODUCING NITROGEN AND HYDROGENivrrx'runns no Drawing. Original application filed. April 29, 1930,Serial No. 448,424. Divided aiid this application I filed January21,1931. Serial No. 510,284. v r

D This invention relates to the production of gaseous mixtures ofnitrogen andhydrogen and more particularly to the production of suchmixtures by the catalytic decomposition of ammonia, as set forth in myco-pending application, Ser. No. 448,424, filed April 29, 1930, of whichthe present application is a division,

It is known that ammonia can be decomposed into its velements, nitrogenand hydrogen, by subjecting it at an elevated temperatrim to contactwith iron." This method of producing nitrogen and hydrogen is used withadvantage where such gaseous mixtures are required for the testing ofthe efliciency of catalysts for the synthesis of ammonia from itelement. Moreover, when employing synthetic ammonia as the raw material,this is a convenient way of readily obtaining hydrogen of a high degreeof purity which may advantageously be employed under circumstances suchthat the presence of the relatively inert nitrogen is of littlediasdvantage.

Iron alone exhibits some activity as a catalyst for the thermaldecomposition of ammonia but when employed for any prolonged period atsuch elevated temperatures, say 500 to 700 C. for example, as aredesirable for the efieotive conduct of the reaction, this materialbecomes powdered and sintered in such a way as to obstruct the passageof gas through the reaction tube. If, therefore, the decomposition ofammonia is to be effected continuously over a long period of time, it isnecessary at rather frequent intervals to replace the iron with freshmaterial.

It is the object of the present invention to provide an improved processfor producing gaseous mixtures of nitrogen and hydrogen by the thermaldecomposition of ammonia, the process being characterized by theemployment of improved catalysts possessing a high degree of activityand capable of use for long periods of time without disintegration.

Other objects and advantages of the invention will be apparent as it isbetter understood by reference to the following specification in whichits details and preferred embodiments are described.

According to the present invention improved resultszare obtained in; theproduction of gaseous mixtures of nitrogenan'd hydrogen by thermaldecomposition of ammonia by combining a catalyst, containingiron-together with one or more oxides ofthe'eles ments comprising thegroups'aluminuni, zir- COI1111II1, chromium, magnesium and calcium. Byemploying catalysts of thiscomposition it is possible to'effect -thedecomposition of ammonia more rapidly andat a lower temperature thanwith iron alone. l T

Although various methods may be used in the preparation of'thecatalyst-and other ingredientsthan those named-above may: also beincluded if desired, 1- have found that for the best resultsthecatalystshould be substantially free from elements of the alkalimetal group or compounds thereof. For,-although the alkali: =metalsjand.their com: pounds are frequently used-with advantage in catalyticcompositions andin fact, due'to the methods and the raw materialscommonly employed in catalyst manufacture one or more of these elementsare likely to be pres ent, my experience has shown that itis advisableto take precautions to avoid the'presence of alkali metals in thecatalyst. In other words, it is preferred to avoid using such methods ofpreparation as would involve, for instance, the addition of vany of thecatalyst ingredients in the form' ofan alkali metalsalt or if suchcatalyst be employed,fto take steps-to eliminate'the alkali metalfromthecatalyst before it-is usedin the decomposition, of ammonia. Thepresence of alkali metal in the catalyst tends to decrease the lifethereof, apparently by sintering and fusing in such a way as to obstructthe free flow of gas through the'body of contact material. 4

The catalysts herein described and methodsfor'the preparation of whichare set forth in-the followingexamples are more active and generallysatisfactory in the thermal decomposition'of ammonia than iron alone. -For example, I have carried on the decomposition of ammonia for as longas -500 hours without;appreciable deterioration of the catalyst.

While various methods of preparing the 2f catalysts may be employed andthe conditions under which they are used in decomposing ammonia may bevaried within wide limits, the following-examples are given'toillustrate the manner-of practicing the invention Example 1.Mix a 10%solution of ferric. sulphate with an equal volume of 10%solutionof'ammonium chromate and'then add ammonium "hydroxide tocomplete precipitation. Filter the precipitate, wash free from sulphatesand dry. .-Form the dried material into briquets of suitable siz andsubject these to reduction by-means of hydrogen at a temperature withinthe range of 300 to 550 C. In employing this catalyst in the thermaldecomposition of'ammonia it isdisposed in a-nickelror nichrome tubesurrounded by an electrical heater. When ammonia gas is pressed overthis catalyst at atemperature within the range of 600 to 700 C. theammonia is decomposed into its elements and'by suitably adjusting therate of flow an eflicient conversion of ammonia to nitrogen and hydrogenmay beobtained. Any undecomposed ammonia may be removedfrom the gaseousproducts by one of the known wayspas, for example, by absorption'inwater oran acid.

Example 2.A catalyst adapted foruse in them'anner indicated underExample 1 may be prepared by adding approximately 3% by weight ofmagnesium oxide and 8% by weight of aluminumoxide to pure ferroso ferricoxide, the percentages being based on thetotal catalytic materialcalculated as oxide; Melt the oxide mixture, allow it to cool andcrushand screen it "to suitable size. The catalyst is subjected toreduction'before-use.

Example 3.The catalyst described in Example 1 may be replaced by oneprepared by fusing ferroso ferric oxide with 2% by weight of'zirconiumoxide. The molten mixture-is allowed'to cool, crushed, screened tosuitable size and then reduced.

No explanation or theory is oifered as to any changes in'physicalform orchemical composition that may occur in the catalyst in the course of itsreduction or during actual use. The term catalyst as employed in theclaims is intended, therefore, to include the contact mass as preparedas well as any modified form in which it may exist during the reaction.It'should also be understood that, sinceit is-generally recognized thatthe activity of substances as catalysts is'a function of the chemicalelements contained therein rather than of the particular type ofcompound employed, the term oxide as employed herein is to beconsideredas including oxides aslsuch or as they may be present inchemical combination with other elements:

While the temperature range of 6007 00 C. indicated in the foregoingexamples represents'" the preferred temperature range, the invention isnot limited'to the utilization of these temperatures. The'reaction canactually be initiated and carried on at lower temperatures, but foreflicient operation of the process I prefer to employ the elevatedtemperatures named; Higher temperatures may also" be employed but,generally speaking, with some deterioration in the physical form of thecatalyst.

Various changes may be'made in the method described without departingfrom the invention or'sac'rificing any of the advantages thereof.

I claim:

1. The process ofproducing a mixture of nitrogen and hydrogen whichcomprises con tacting gaseous ammonia at an elevated ternperature With acatalyst comprising iron and zirconium oxide.

2. The process of .producing a mixture of nitrogen and hydrogenwhich'comprises contacting gaseous ammonia at a temperature within therange of 600 to 7 00 C..with a catalyst comprising iron and zirconiumoxide.

3. The process of producing a mixturev of nitrogen and hydrogen whichcomprises contacting gaseousammonia at an elevated temperature withacatalyst consisting of iron and zirconium oxide, said catalyst beingsubstantially free from alkali metal.

In testimony whereof, I affix my signature.

RALPH -L'. DODGE.

